The present invention relates generally to material separating devices for separating particulate materials of different specific gravities and relates particularly to a device for separating heavier foreign matter from low specific gravity stock such as wood chips and the like. More particularly, this invention relates to an improved drainage chamber for a material separating device.
In the processing of paper pulp, wood chips or sawdust are passed into refiners to break down the material into fibrous pulp for subsequent processing. Prior to the refining operation, foreign matter must be removed from the stock, and the water content of the stock must be as low as possible. One of the conventional prior art apparatus employed for this purpose is described in Canadian Patent No. 966,449. In such apparatus, a housing is provided enclosing a settling chamber, an adjacent drain chamber and a discharge chamber. An agitating and conveying screw passes horizontally through the settling chamber and drain chamber, terminating adjacent the discharge chamber beyond the drain chamber. Means are provided for maintaining a water flow from the lower region of the settling chamber, which water flow continually immerses a portion of the conveyor screw and passes into the drain chamber. Material to be separated is introduced into the upper region of the settling chamber wherein it is washed by the water flow and agitated and conveyed by the water and conveyor toward the drain chamber. A U-shaped screen disposed in the drain chamber serves to separate the fine foreign matter from the stock and also to remove the water from the stock. The stock is then discharged into pulp refining equipment without further treatment.
In the prior art apparatus, the screen means disposed in the drain chamber is generally a U-shaped screen that is supported beneath the screw conveyor. The U-shaped screen is non-movable and is attached to the housing of the drain chamber. Additionally, the screw conveyor of the prior art apparatus is of uniform flight size. The screw conveyor extends from the settling chamber through the drain chamber and to the discharge chamber and is of substantially the same size of flights throughout the length. Although drain chambers having the above configuration will work, they are not as effective as desired. The drainage rate of the material to be pulped is not as efficient as necessary and too much water is discharged into the pulp refining equipment. If the speed of the screw conveyor is slowed down to reduce the amount of water being discharged to the refining equipment, the amount of material to be pulped is reduced to an uneconomical rate.
It is accordingly an object of the present invention to provide an improved material separator for separating materials of different specific gravity. In particular, it is an object of the present invention to provide an improved material separator for separating foreign matter from wood chips, saw dust and other pulping material prior to pulping the material. It is particularly an object of the present invention to provide an improved drain chamber for a material separator for separating materials of different specific gravity.